Cotton growers commonly apply nitrogen (N) fertilizer at rates of between 100 and 200 kg N/ha, yet the cotton plants seldom recover more than 40% of the applied N, and often much less. What happens to the fertilizer N not recovered in the plants? Some of it remains bound in the soil, and part of this may gradually become available to succeeding crops. Some of it is probably lost to the atmosphere in gaseous forms. Some of it may be leached below the root zone; however, on heavy clay soils, leaching is not generally considered to be an important N loss mechanism. Gaseous N losses. The major gaseous N loss forms are ammonia (NH3), dinitrogen (N2} and nitrous oxide (N20).